Body Fat Calculator

1. 01Measure neck, waist, height, and (for the female formula) hipUse a flexible tape measure, snug but not compressed, in centimeters. Neck below the larynx; waist at the navel (men) or narrowest point (women); hip at the widest point (women).
2. 02Choose male or femaleThe Navy method uses two different formulas — the female version also requires a hip measurement, the male version does not.
3. 03Read the estimate, with its margin of error in mindTreat the result as a general estimate, not an exact number — see the accuracy notes below.

• Tracking body composition changes over timeSince the formula is consistent, repeating the same measurement method periodically can show a trend, even if any single reading has some margin of error.
• Getting a body-fat estimate without special equipmentUnlike skinfold calipers, bioelectrical impedance scales, or DEXA scans, this method only needs a tape measure and a formula.
• Understanding a Navy-method figure from another sourceIf you have already seen a "Navy body fat" number from a fitness app or program, this tool shows exactly how that number is calculated and where its limitations come from.

• A male exampleNeck 38.1 cm, waist 86.4 cm, height 177.8 cm produces an estimated body fat of about 11.1% under the Navy formula.
• A female exampleNeck 33 cm, waist 76.2 cm, hip 101.6 cm, height 165.1 cm produces an estimated body fat of about 7.6% under the Navy formula — illustrating the calculation, not a typical or target value.
• Why the formulas differ by sexThe female formula includes a hip measurement and uses different constants, because the original 1984 validation study found that circumference-to-body-fat relationships differ meaningfully between men and women.

The formula was developed by Hodgdon and Beckett in 1984 by comparing circumference measurements against underwater weighing (hydrostatic density measurement), which was then considered a reliable body-composition reference method. The result is a regression formula: Men use waist and neck; women use waist, hip, and neck; both also use height. It is not itself a direct measurement of body fat — it is a statistical estimate calibrated to match hydrostatic-weighing results as closely as possible in the original study population.

Even with careful, consistent tape measurement, the Navy method typically carries a margin of error commonly cited around ±3-4 percentage points compared to more direct methods like DEXA scans. Measurement technique matters a lot — where exactly the tape sits, how snug it is, and consistency between measurements all affect the result. The formula's accuracy for people who differ substantially from the original study population (in age, ethnicity, or athletic muscularity) is also less certain than for a typical adult similar to that population.

Body fat percentage is one indicator among many, and this formula is a practical estimation tool, not a medical or diagnostic measurement. For a more precise reading, dedicated methods like DEXA scans, hydrostatic weighing, or air-displacement plethysmography are more accurate — but also far less accessible than a tape measure.

How accurate is the US Navy body fat method?

It is a validated estimation formula, not a precise measurement — commonly cited as accurate to within roughly ±3-4 percentage points compared to more direct methods like DEXA scans, assuming careful and consistent tape measurement.

Why does the female formula need a hip measurement but the male one does not?

The original 1984 Hodgdon and Beckett study found different circumference-to-body-fat relationships for men and women, and the female regression formula that best matched hydrostatic-weighing results included hip circumference; the male formula did not need it to fit the data as well.

Can I use this to track progress over time?

Yes, as a trend indicator — since the method and its margin of error stay consistent, repeated measurements with the same careful technique can show a meaningful direction of change, even though any single reading has some uncertainty.

Why did I get no result?

The formula requires waist to be greater than neck (and, for the female formula, waist plus hip to be greater than neck) — if your measurements do not satisfy that, or produce an implausible result, double-check your tape measurements and try again.

Is my data saved?

No. Everything is calculated in your browser; nothing is sent to a server.